This invention relates generally to testing printed circuit boards and more particularly concerns a fixture and test method for measuring the force and deflection required for breaking apart printed circuit boards along a pre-existing score line.
In manufacturing electronic equipment, manufacturers in an effort to save labor costs, have adopted automated machinery that inserts electric components into printed circuit boards. As the sophistication and capital costs of such automatic component insertion machines increase, it is important that those machines be utilized at maximum efficiency. Particularly, the efficiency of such machines can be increased if the machine can process a small number of large printed circuit boards instead of processing a larger number of small printed circuit boards. Such increase in efficiency results from eliminating some of the lost time that occurs while loading the printed circuit board without components into the machine and removing the printed circuit board with components from the machine.
In order to maximize the size of the printed circuit boards being processed, a single large printed circuit board can be provided with the circuitry and space for number of smaller circuit boards thereon. Once the components have been inserted by the automatic insertion machine, the large printed circuit board is separated into the several small circuit boards. In order to separate the larger circuit board into smaller circuit boards after the parts have been inserted, score lines are cut on the large printed circuit board before the components are inserted so that the large printed circuit board can be broken apart and separated along the previously cut score lines.
In order to assure consist and clean breakage of the printed circuit boards along the score lines, it is necessary that the board material (the web) between the score lines provided on each side of the board be of uniform thickness. U.S. Pat. No. 4,856,400 in the name of the applicant herein, discloses a particularly advantageous scoring cutter which provides a uniform depth score lines and a uniform thickness web along which the printed circuit board can be broken.
In the assembly of circuit components on printed circuit boards, the circuit boards must be held in a precise location during machine assembly and soldering. When the process is finished, the boards must break apart without excessive flex which would cause the soldered components to break or lift from the soldered paths. At the same time, the web between the score lines must be strong enough to withstand the forces of the component insertion machine without premature separation.
It is therefore necessary to establish statistical values for the force required to break apart the circuit boards along the pre-existing score lines and for the amount of flex experienced by the circuit boards during separation. Particularly, when a circuit board under test is clamped and broken along a score line, the circuit board should not flex more than 0.030 inch per inch of distance from the clamp (the overhang). In addition, the force required to break apart the circuit board along the score line should be between two and six pounds per lineal inch of score line with three pounds per lineal inch of score line being the nominal target value.